Duchenne muscular dystrophy is caused by mutations of the dystrophin gene. The dystrophin gene is 3000 kb in size and consists of 79 exons encoding a 14-kb mRNA.[2,3] At least eight alternative promoters that are regulated in a tissue- or development-specific manner have been identified on the dystrophin gene. The unusually high incidence of DMD in all human populations could be simply a reflection of the enormous mutation target size of the gene, but the recombination rate is reported to be four times the rate expected for a gene of this size. Nearly two-thirds of mutations identified on the dystrophin gene are deletions or duplications occupying a single or multiple exons, with the rest of the DMD cases having other types of mutations including point mutations. Remarkably, deletion mutations have been localized to two deletion hot spots of the dystrophin gene, the 5' and the central regions.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.